Leonardo DiCaprio as Rick Dalton: An actor who starred in the Western television series Bounty Law from 1958 to 1963. His attempt to transition to movies has not worked out and in 1969, he is struggling, doing guest roles on other people's programs while contemplating moving to Italy, which has become a hotbed for low-budget Westerns. He is a neighbor of Sharon Tate.

Emile Hirsch as Jay Sebring: A Hollywood hairstylist and friend of Sharon Tate who was murdered in Tate's home by followers of Charles Manson.

Damian Lewis as Steve McQueen: An actor and friend of Jay Sebring, who was invited by him to Sharon Tate's home for a dinner party the night of the Tate murders, but he was unable to show up.

Bruce Dern as George Spahn: An 80-year-old nearly blind man who rented his Los Angeles ranch out to be used as a location for Westerns. Manson convinced Spahn to allow him and his followers to live on the ranch, in the months before they murdered Sharon Tate and six others. In exchange for rent, Manson coerced his female followers into having sexual relations with the ranch owner, and serving as his seeing-eye guides. Burt Reynolds was initially cast in the role, but died before his scenes could be filmed.[6][7]

Spencer Garrett as Allen Kincade: The television personality and interviewer to Hollywood’s elite.

Mike Moh as Bruce Lee: The international actor-stuntman who choreographed fight scenes for The Wrecking Crew, which starred Sharon Tate. Following the Tate murders, Lee attended her funeral and was also privately investigated.

On July 11, 2017, it was announced that Quentin Tarantino had written a screenplay for a film about the Manson Family murders, which he would direct as his next project. Harvey and Bob Weinstein would be involved but it was not known whether their studio, The Weinstein Company, would distribute the film as Tarantino sought to cast the film before sending out a package to studios. Brad Pitt and Jennifer Lawrence were revealed to be two names Tarantino had approached to star in the film.[10] On the same day, it was separately reported that Margot Robbie was in talks to potentially portray actress Sharon Tate, Samuel L. Jackson was also in talks to portray a major role, and that Pitt was in talks to portray the detective investigating the murders.[11]

In the wake of the Harvey Weinstein sexual abuse allegations, Tarantino severed ties with Weinstein and sought a new distributor, after having worked with Weinstein for his entire career. At this point Leonardo DiCaprio was revealed to be among the actors Tarantino was considering for the film.[12] A short time later, there were reports that the studios were still bidding for the film set in Los Angeles in the late 1960s and early 1970s, that Tom Cruise was also in talks for one of two lead male roles, and David Heyman had joined the film as a producer, who would produce along with Tarantino and Shannon McIntosh.[13] On November 11, 2017, Sony Pictures announced they would be distributing the film, having beaten Warner Bros., Universal Pictures, Paramount Pictures, Annapurna Pictures and Lionsgate for the rights.[14] In order to secure the rights to distribute the film, Sony Pictures had to agree to Tarantino's demands, which included "a $95 million production budget, final cut and "extraordinary creative controls," plus 25% of first-dollar gross.[15] Another demand was that the rights to the movie revert to him after 10 to 20 years."[16] During a publicity interview by The Hollywood Reporter, Margot Robbie, when inquired about her potential involvement in the Tarantino-helmed film, noted that "Nothing's official … but I would kill to work with him."[17]